Conventional sewer systems which are utilized to service large metropolitan areas invariably employ concrete sewer lines from 8 inches to over 12 feet in diameter. These concrete sewer lines are installed below ground level at depths of about from 3 feet to over 30 feet and may extend for hundreds of miles in a variety of directions. The initial cost of installation can be as much as $2,000.00 per linear foot, and therefore, to make such a system cost-effective, it is desirable that its useful life be as long as possible, for example, about 100 years or longer.
However, there is a great prevailing problem, in existing systems, of deterioration of the inner walls of the concrete sewer conduits, particularly in the upper region of the pipe interiors where washing of the wall surfaces by the flow of sewage does not take place. The degree of deterioration of the concrete conduits varies from loss of surface cement to total loss of top of the pipe so that the overlying soil collapses into the sewer. Such deterioration has been found to be caused by certain bacteria which are commonplace in sewer systems. The bacteria, which collect and colonize on unwashed interior wall surfaces, take in hydrogen sulfide and oxygen and convert it to sulfuric acid (H2SO4), which causes erosion of the wall surface on which the bacteria have collected. While the deterioration of such wall surfaces is a very slow process, the degree of deterioration of concrete sewer conduits is such that within 30 to 50 years after installation, such systems require major repairs or replacement of significant lengths of the conduits.